This invention relates to a method and apparatus for determining the presence of a magnetic storage medium such as an iron oxide or chromium oxide layer on a tape such as audio or video recording tape. Specifically the method and apparatus according to the embodiment disclosed in this application is used to ensure that tape which is wound on a supply package and loaded on a high speed cassette winder has been wound with the oxide layer on the proper side of the tape to be correctly wound into the cassette for future playback and recording. While the invention disclosed herein is discussed with specific reference to a high speed cassette loader, it also has application on tape winders, slitters and high speed tape duplicators.
In order for a cassette to be usable, the tape must be properly oriented so that the oxide layer faces to the outside so it can come into contact with the recording and playback heads of a tape deck. High speed cassette loaders are capable of loading an empty cassette with either blank or prerecorded tape in only a few seconds. Therefore, placing an improperly wound supply package of tape on a cassette winder can very quickly waste a considerable number of cassettes and a substantial amount of machine productivity.
With modern audio and video recording tape, it is difficult to determine visually whether the tape is oriented correctly side-to-side. In order to put as much tape as possible in a cassette, the tape itself is made ultra-thin. Advances in oxide coatings have reduced the thickness of the oxide layer to the point where it may be substantially transparent. Therefore, a highly polished oxide layer on an ultra-thin transparent tape may look virtually the same on both sides.